1. Field of the Invention
The invention relates in general to a method for reading a memory and a memory, and more particularly to a memory reading method capable of enlarging the read window and reducing the read disturbance and a memory using the same.
2. Description of the Related Art
Memories are now applied to various data storage purposes and are classified into many types, one of which is a multi-level cell (MLC) memory. FIG. 1A (Prior Art) is a schematic illustration showing a conventional multi-level cell 100. Referring to FIG. 1A, the multi-level cell 100 includes a left half cell 110 and a right half cell 120. Each half cell of the multi-level cell 100 may have many bits according to different threshold voltage distributions.
Illustrations will be made by taking each half cell having two bits as an example. FIG. 1B (Prior Art) is a graph showing the threshold voltage distributions of the multi-level cell 100. The threshold voltage distributions of the left half cell 110 and the right half cell 120 are usually and sequentially defined as, without limitation to, (11, 10, 01, 00). Each threshold voltage distribution in FIG. 1B has to be possibly concentrated to keep the sufficient read window.
However, the threshold voltage of the right half cell 120 is influenced by the threshold voltage of the left half cell 110 due to a second-bit effect. So, the read window is decreased to cause an error when the right half cell 120 is being read. In addition, if a bit line voltage or a word line voltage for reading is too high, a low threshold voltage of the left half cell 110 may be influenced so that a read disturbance phenomenon may occur when the left half cell 110 is being read.